The present invention relates in general to heat pipe technology, and in particular to a parallel-plate heat pipe having a plurality of curvilinear capillary grooves for transferring a working fluid in a liquid state from a condenser region to an evaporator region. The present invention allows multiple heat sources to be located on the parallel-plate heat pipe and minimizes the possibility of heat-source shadowing.
A heat pipe provides a light-weight efficient passive means of transferring heat from a heat source to a heat sink. Heat pipes are currently used for heat removal or heat transfer in many applications including the cooling of electronics. A particular application of heat pipes is for cooling of integrated circuitry in high-density microelectronics and laptop computers.
One problem that arises when using heat pipes to cool integrated circuitry (also termed semiconductor chips) is that, when multiple chips are thermally coupled to a conventional heat pipe for cooling, there is the possibility for xe2x80x9csource shadowingxe2x80x9d in which the heat removed by a first semiconductor chip and transported to a heat sink by the heat pipe and the resupply of a working fluid to the location of the first chip by capillary action interferes with and can diminish the removal and transport of heat from a second semiconductor chip and the resupply of the working fluid to the location of the second chip. Under certain heat loadings, this can lead to a localized xe2x80x9cdryoutxe2x80x9d of the working fluid in the heat pipe at the location of the second chip, resulting in an unacceptable rise in the temperature of the second chip which can affect its performance and reliability. As an example, when such a conventional heat pipe is used in a computer, this heat-source shadowing can limit the speed of operation of certain chips and thereby slow down operation of the computer.
The present invention provides a solution to this problem by providing a heat pipe in which a plurality of evaporator regions each used to transfer heal away from a heat source (e.g. a semiconductor chip) are independently resupplied with a quantity of a working fluid in a liquid state to prevent or mitigate any heat-source shadowing.
An advantage of the present invention is that multiple heat sources can be optimally cooled by a single heat pipe having a plurality of shaped capillary wick structures independently resupplying the working fluid in the liquid state to multiple evaporator regions at the locations of the various heat sources.
A further advantage is that a flow of the working fluid in the liquid state to each evaporator region can be sized according to the amount of heat to be transferred from a heat source at that location.
Yet another advantage is that a flow of the working fluid can be provided between a pair of major inner surfaces within the heat sink of the present invention so that performance of the heat sink is largely independent of orientation (i.e. independent of effects due to gravity).
These and other advantages of the present invention will become evident to those skilled in the art.
The present invention relates to a parallel-plate heat pipe apparatus, comprising a hollow sealed container having a pair of substantially parallel major outer surfaces, and further comprising a pair of substantially parallel major inner surfaces within the container. A plurality of evaporator regions are located on one or both of the major inner surfaces of the container, with each evaporator region being spaced apart from an adjacent evaporator region. A condenser region is located within the container proximate to an edge of one of the major inner surfaces; and a working fluid is disposed within the container for transferring heat from each evaporator region to the condenser region wherein the working fluid is condensed from a vapor state to a liquid state. The heat pipe further includes a plurality of shaped capillary wick structures formed within the container on one or both of the major inner surfaces of the container, with each capillary wick structure further comprising a plurality of curvilinear capillary grooves to provide a capillary flow of the working fluid in the liquid state from the condenser region to one of the plurality of evaporator regions. According to the present invention, the container can comprise a metal (e.g. copper or aluminum) or a semiconductor (e.g. silicon); and the working fluid can comprise, for example, water or methanol. A metal container can be assembled, for example, from a pair of substantially parallel flat or curved plates welded at the edges thereof to an intervening annular metal spacer.
The capillary grooves preferably follow calculated curvilinear fluid-flow paths between the condenser region and one of the evaporator regions, with the fluid-flow paths preferably being determined from a solution of Laplace""s Equation. The number and dimensions of the capillary grooves within each capillary wick structure can be selected according to a quantity of the working fluid in the liquid state to be transferred from the condenser region to each evaporator region. Each curvilinear capillary groove can be formed, for example, from an electroplated metal. Additionally, to prevent clogging of the flow of the working fluid in the capillary grooves, a plurality of interconnections (i.e. openings) can be formed between adjacent capillary grooves within each capillary wick structure to permit the transfer of the working fluid in the liquid state between the adjacent grooves.
A plurality of support posts can be provided inside the container for rigidity, with each support post generally being attached at each end thereof to one of the major inner surfaces of the container (e.g. by resistance welding). The support posts can comprise a metal (e.g. copper or aluminum) or a semiconductor (e.g. silicon). An optional annular wick structure can also be provided within the container to provide a fluid pathway between the major inner surfaces of the container for the working fluid 110 in the liquid state. The annular wick structure can comprise a sintered metal felt (e.g. comprising stainless steel), and can be located proximate to the support posts or proximate to an inside edge of the container.
The present invention also relates to a parallel-plate heat pipe apparatus for transferring heat away from a plurality of heat sources, comprising a sealed container having an evaporator region superposed below each heat source, and a condenser region located proximate to an edge of the container; a working fluid disposed within the container for transferring heat from each evaporator region to the condenser region in a vapor state; and a plurality of spaced-apart curvilinear capillary grooves connecting the condenser region to each evaporator region for returning the working fluid in a liquid state to the evaporator region to replace any of the working fluid evaporated therefrom. The capillary grooves, which are generally interconnected, can comprise an electroplated metal, or alternately can be etched into the material (e.g. a metal such as copper or aluminum, or silicon). The working fluid can comprise water or methanol. The heat pipe container can further include one or more spacers located between a pair of opposing major inner surfaces of the container; and a sintered metal wick structure can be optionally located within the container to provide a path for the working fluid as a liquid between the opposing major inner surfaces of the container.
The present invention also relates to a parallel-plate heat pipe apparatus for conducting heat from a heat source to a heat sink that comprises a pair of substantially parallel plates connected together to form a hollow sealed container. An evaporator region is located on a portion of a major inner surface of one of the pair of parallel plates proximate to where the heat source is to be attached; and a condenser region is located within the container proximate to a side of the container where the heat sink is to be attached. A working fluid is disposed within the interior of the container for transferring heat from the evaporator region to the condenser region in a vapor state. A plurality of capillary grooves are formed on the major inner surface on one or both of the parallel plates to transfer the working fluid in a liquid state by capillary action from the condenser region to the evaporator region. These capillary grooves are preferably arranged along paths defined by a calculated flow of the working fluid in the liquid state; and a majority of the plurality of capillary grooves are curvilinear.
The amount of the working fluid loaded into the heat pipe can be precisely determined by completely filling the container with the working fluid, and using a timed evacuation procedure to remove a portion of the working fluid from the container. The parallel-plate heat pipe can further include a plurality of support posts located between the pair of plates and attached at each end thereof to one of the pair of the plates (e.g. by resistance welding). Additionally, a sintered metal wick structure can be located within the container (e.g. proximate to each support post, or proximate to one or more inside edges of the container) to provide a flow path for transfer of the working fluid in the liquid state between the pair of plates. A timed evacuation procedure can be used to load a predetermined quantity of the working fluid into the heat pipe.
Additional advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following detailed description thereof when considered in conjunction with the accompanying drawings. The advantages of the invention can be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.